Cases are opinions written by judges explaining their decisions. A case will usually contain a statement of the facts and apply the law to those facts. Analysis of a case can help you predict how that court will rule on a similar issue.
Under stare decisis, or precedent, courts in one jurisdiction must follow the rulings of law from previously decided cases in the same jurisdiction. Courts not in the same jurisdiction may be influenced by decisions, but are not bound by them.
Typically, published cases are from intermediate appellate courts and Supreme Courts. Most trial court decisions are not published.